The circumstellar envelope of ζ Tauri through optical interferometry

We present optical interferometric observations of the Be star ζ Tauri obtained using the Navy Prototype Optical Interferometer (NPOI). The multichannel capability of the NPOI allows a high-quality internal calibration of the squared visibilities corresponding to the Ha emission from the circumstellar environment. The observations suggest a strong departure from circular symmetry and thus are described by an elliptical Gaussian model. We use a nonlinear least-squares fit to the data to obtain the likeliest parameters, and the corresponding uncertainties are determined using a Monte Carlo simulation. We obtain 3.14 ± 0.21 mas for the angular size of the major axis, -62°.3 ± 4°.4 for the position angle, and 0.310 ± 0.072 for the axial ratio. By comparing our results with those already in the literature, we conclude that the model parameters describing the general characteristics of the circumstellar envelope of ζ Tau appear to be stable on timescales of years. We also compare our results with the known parameters describing the binary nature of ζ Tau, and we conclude that the envelope surrounds only the primary component and is well within its Roche lobe.